In response to the increasing capacity of flash memory, a type of storage device, and to expansion of the market for image sensors or the like designed for high-resolution cameras in mobile phones and smartphones, there arises a strong demand for further micropatterning in semiconductor devices. In the manufacture of these various electronic devices, photolithographic techniques are used widely. In photolithography, efforts have been made to facilitate micropatterning by using a light source of shorter wavelength. When a KrF excimer laser or a short wavelength light source developed thereafter is used as a light source, chemically amplified resists are used in most cases and they are generally configured in the form of solutions containing a functional resin serving as a base material and a photoacid generator and further containing several types of additives. Among these components, a functional resin serving as a base material is a determinant of resist performance and it is important for such a functional resin to have a good balance of various properties including etching resistance, substrate adhesion, transparency against a light source to be used, development speed, etc.
Functional resins for use in photoresists for KrF excimer lasers are usually polymers comprising, e.g., a vinyl compound or acrylate as a repeating unit. For example, hydroxystyrenic resins have been proposed in the case of resists for KrF excimer laser lithography (Patent Document 1), while acrylic resins whose backbone is composed of adamantyl (meth)acrylate have been proposed in the case of resists for ArF excimer laser lithography (Patent Documents 2 to 6); and hence the required backbone is now being fixed. However, polymers composed of a single type of repeating unit are not used for this purpose. This is because a single type of repeating unit cannot satisfy all of the properties including etching resistance. In actual cases, several types, i.e., two or more types of repeating units having functional groups required to improve the individual properties are used for copolymerization to give a functional resin, and the resulting functional resin is further blended with a photoacid generator and others and dissolved in a solvent for use as a photosensitive resin composition. Moreover, heat-curable compositions known for use as photoresists or the like include those comprising hemiacetal ester derivatives (Patent Documents 7 and 8). However, since photoresists are generally heated at around 100° C. to 150° C. after pattern exposure (post-exposure bake), there is a concern that the hemiacetal skeleton will be thermally decomposed at 100° C. or higher temperatures (Patent Document 9 and Non-patent Document 1).
Recent lithographic processes have further facilitated micropatterning. ArF excimer laser lithography has continued to progress from liquid immersion exposure to double patterning exposure, while various efforts have also been made to develop extreme ultraviolet (EUV)-based lithography, which receives attention as a next-generation lithographic technique, as well as direct writing with electron beams and negative tone development. Under these circumstances, there is a demand for the development of a new functional monomer suitable for micropatterning.